Some vehicles, such as tractor or semi-tractors, include on-board tire inflation systems for maintaining and/or adjusting the inflation of its tires. For example, tire inflation can be adjusted from the cab of the semi-tractor in accordance with the terrain over which the semi-tractor is driving. Also, tire inflation can be maintained at a specified value or within a range of specified values over a period of time to maximize fuel economy of the semi-tractor.
Central Tire Inflation Systems (commonly called CTIS systems) are commonly installed in military vehicles to allow the operator to quickly tailor the vehicles' tire inflation pressures to match the road conditions via a control panel located in the cab. These CTIS systems tie all the vehicles tires, via pneumatic lines, to a central air compressor that has enough capacity to quickly inflate all a vehicle's tires from a low pressure (e.g., 20 psi) used in soft sand to a high inflation pressure (e.g., 100 psi) suitable for high speed travel on a smooth highway. Modified versions of the military CTIS system have been adopted by the civilian market to maintain tires on a vehicle at an optimal pressure to maximize fuel economy and tire life while operating at high speed on a smooth highway. The typical civilian CTIS systems, like the military versions, have a high maintenance union that couples each tire to a non-rotating pneumatic line. The maintenance costs to ensure leak-free operation of multiple rotating unions and pneumatic line connections in typical civilian CTIS systems often outweigh the operational savings.